The present invention relates to a display apparatus adapted for obtaining pseudo-three-dimensional images, particularly for obtaining dynamic pseudo-three-dimensional images as if such images were observed under an endoscope when the endoscope was moved.
There is a technique in which X-ray computerized tomographic images are stacked up to thereby construct a stacked three-dimensional image (hereinafter referred to as "three-dimensional original image") so that the stacked three-dimensional image is directly displayed on a two-dimensional screen or a projection image obtained by projecting the stacked three-dimensional image onto a projection plane from a certain view point is displayed. The technique is directly used for inspection, diagnosis and surgery or used for supporting them. The technique is also applied to any field other than X-ray computerized tomographic images, in which a three-dimensional image measured three-dimensionally by an MRI apparatus is developed into two-dimensional tomographic images to be used as X-ray computerized tomographic images.
For projection onto a projection plane, there are a parallel projection method and a central projection method. The parallel projection method has been described in IEEE CG & A, January (1985), pp. 52-60. The central projection method is superior in that a projection image is obtained as if the image was observed under an endoscope. The detail of the central projection method is disclosed in U.S. patent application Ser. No. 374,088 which has one inventor in common with the present application and is assigned to the same assignee as the present application. In U.S. patent application Ser. No. 374,088, there are shown the significance of updating of a view point, the way thereof and examples thereof in the case where the view point is updated as if observation was made under an endoscope while the endoscope was moved.
The updating of the view point in U.S. patent application Ser. No. 374,088 can be performed relatively easily if a method of giving coordinates of the view point to be updated in advance or a method of setting the coordinates by using a data input means such as a keyboard is used. It is however difficult to update the view point by using a cursor, or the like, on a display screen while an image displayed on the display screen by a central projection method is watched. Assume now that, for example, an image of a human bronchial tube in a depth direction of from the front to the back is obtained by a central projection method and displayed. Because the distance in the depth direction is not displayed on the screen, it is impossible to set a new view point in the depth direction at a predetermined distance accurately.
Accordingly, in order to make it possible to set the position of the new view point accurately on the display screen, it is necessary that an image effective for updating the view point is displayed.